1. Technical Field of the Invention
The present invention relates to a switching method and equipment, wherein a serial bus is connected with extension nodes having asynchronous interfaces and isochronous interfaces for switching signals between an outside line and extension lines and between the extension lines.
2. Description of the Prior Art
Conventionally, switching devices for home use are simple, because they are provided merely with an analogue or digital voice switch. Recently, however, information devices such as personal computers have been introduced into the home, and digital broadcasting has become popular. Therefore, there are growing needs for distributing image signal, data signal, voice and audio signal to an individual or to individuals simultaneously.
Therefore, asynchronous transfer mode (ATM) and local area network (LAN) such as Ethernet are improved for distributing time series data such as audio-visual signal.
Further, IEEE 1398 (IEEE Std. 1394-1995 IEEE Standard for a High Performance Serial Bus) is known by its real time and high speed performance, and plug-and-play capability. Therefore, IEEE 1394 can be used in a high speed network for multi-media signal into the home. IEEE 1394 applied to the home telephone is exemplified in FIG. 15. As shown in FIG. 15, digital voice signal 601 loaded at step 602 on IP packet (Internat Protocol packet) 603 is transmitted at steps 604, 605 by asynchronous transfer on IEEE 1394 bus 301 toward a person on the other end of the line. Voice signal 601 is recovered by disassembling the IP packet 603 and reassembling them at step 602 to become the audio signal 601 at the receiving end. Such a telephone system as explained above simply is called IP telephony defined by ITU-T H323.
However, ATM costs much, and Ethernet architecture can not guarantee the real time performance for a plurality of time series data streams.
On the other hand, home use switching equipment for voice, audio-video signals must be of low cost. In addition, it must have complete plug-and-play capability, when appliances are newly installed.
Actually, the IP telephony on IEEE 1394 as well as the IP telephony on the internet requires additional competent software, CPU, and hardware, such as codec for DSP (digital Signal Processing).
However, completely natural voice is hardly obtained in general by the IP telephony, because the time series data stream is processed by asynchronous system.
Further, in an advanced network, the plug-and-play capability is indispensable for automatic recognition of newly installed appliances.
The connection route is changed often or even stopped by a bus reset on IEEE 1394 for plug-and-play. However, the communication should not be interrupted by such a bus reset.
Furthermore, the communication quality should be maintained under fluctuations in data traffic.
Further, it is desirable to provide such an advanced network with API (Application Program Interface) compatible with various operating systems and protocols.
Further, each terminal can identify other terminals by their ID numbers under the plug-and-play circumstance.
Furthermore, it is desirable to provide a telephone equipment with such functions as master-slave communication, slave—slave communication, master-slave transfer, and slave—slave transfer.